It is known that, when provided with conductive layers, stretched polylactic acid films can be used as piezoelectric polymer materials (Patent Documents 1 and 2). It is also known that, by laminating such piezoelectric polymer materials to form a bimorph or multimorph structure, thereby enhancing piezoelectric properties, it is made possible to use them as vibrating bodies of microphones, pickups, buzzers, speakers, optical switches, fans, etc. or as piezoelectric actuators (Patent Documents 3 to 5). However, Patent Document 3, in which piezoelectric polymer films are bonded together with an adhesive, suffers from complicated processing steps such as lamination etc. and from low productivity. A method of forming a bimorph structure by co-extrusion is known to solve these problems (Patent Document 6).
On the other hand, in the field of materials for presentation packaging of commercial products and the like, which is a wholly separate field from piezoelectric polymer materials, it is known to incorporate a poly(meth)acrylate-based resin in polylactic acid and to incorporate an impact modifier in it to provide a polylactic acid-based resin laminated sheet with excellent heat resistance, transparency, and impact resistance (Patent Document 7).